if you use the VBM8 modulation for non-linear terms only the TIV is considered by a globally scaling your segmentations with the scaling factor from the affine spatial registration. The affine scaling factor correlates very well with the TIV, see http://www.freesurfer.net/fswiki/eTIV for more information on this topic.
On Fri, 25 Sep 2015 07:40:08 +0100, Ellen <[log in to unmask]> wrote:
>Hi all, I am new to VBM and teaching myself so apologies if this question is very basic. Do I need to covary for total intercranial volume (TIV) if I use the VBM8 toolbox to preprocess the images? I will be doing a statistical comparison between two groups (schizophrenia vs control). I have heard mixed things. Someone mentioned that this pipeline process will take care of TIV as it normalises within each subject individually however others have told me that I still need to covary for TIV if I am doing a between-groups comparison.